An optical fiber cable generally comprises two or more optical fibers enclosed within a sheath or jacket. To accommodate demand for increased bandwidth without substantially increasing the cable diameter, the fiber count and fiber packing density may be increased. Optical fiber cables having high fiber counts and packing densities may present manufacturing challenges.
In an optical fiber cable, fibers or groups of fibers are commonly twisted together (also referred to as “stranded”) to equalize strain. Loose or disorganized fibers are susceptible to undesirable interaction with each other during cable manufacturing and handling that can produce local areas of small-radius bending, resulting in undesirable signal attenuation. Optical fiber cables having only non-twisted fibers are not common and are generally limited to cables combining the characteristics of low fiber count, low packing density, and features that help minimize strain. An example of a cable having only non-twisted fibers is disclosed in U.S. Pat. No. 4,971,419 to Gartside et al.
An optical fiber ribbon comprises two or more parallel optical fibers that are joined together along their lengths. A material commonly referred to as a matrix adheres the fibers together. In a “flat” (also referred to as “encapsulated”) type of optical fiber ribbon, the fibers may be fully encapsulated within the matrix material. The rigidity of encapsulated optical fiber ribbons presents challenges to achieving high fiber packing density in cables. So-called “rollable” optical fiber ribbons have been developed to achieve high fiber packing density in cables. In a rollable ribbon the matrix material is intermittently distributed along the fibers, providing sufficiently flexibility to roll up each individual ribbon about an axis parallel to the fibers or otherwise compact the ribbon into a fiber bundle with a roughly cylindrical shape. Two or more rollable ribbons can be grouped together into a compact bundle parallel to the axis of the fibers.
A machine known as a mass fusion splicer can splice two ribbons without requiring an operator to separate the individual fibers in the ribbons, thereby saving time. Due to the convenience of mass fusion splicing, ribbons are generally preferred over separate (i.e., “loose”) fibers for high fiber count ribbons.
A conventional optical fiber cable structure may comprise two or more optical fiber ribbons that are twisted together. Techniques known in the art can be employed that achieve high packing densities, including, for example, packaging twisted ribbons or bundles of twisted ribbons in central tube or slotted cable structures.